1. Field of the Invention
One embodiment of the invention relates to a light source module provided with a plurality of semiconductor light emitting elements configured to emit light together and a lighting apparatus comprising the light source module.
2. Description of the Related Art
Conventionally known are LED light source units that comprise a plurality of light emitting diode (LED) bare chips configured to emit blue or ultraviolet light. In an LED light source unit described in Jpn. Pat. Appln. KOKAI Publication No. 2004-193357 (Patent Document 1), a plurality of LED bare chips are regularly mounted on a metal base printed board. A conductor pattern is formed on an insulating layer of the printed board. The bare chips are connected to the conductor pattern. A reflector is located on the metal base printed board. The reflector comprises a plurality of tapered holes that accommodate the bare chips, individually. Each hole is filled with a translucent sealing resin mixed with phosphor powder.
The LED light source unit described in Patent Document 1 is used as a planar light source in which the bare chips are caused to emit light together. The blue or ultraviolet light emitted from each bare chip is changed into white light by the phosphor powder as it is transmitted through the sealing resin. This white light serves for illumination when its projection direction is regulated by the respective inner surfaces of the tapered holes of the reflector that is much thicker than each bare chip.
An LED light source unit comprising neither a phosphor nor reflector is also described in Patent Document 1. In this LED light source unit, LED bare chips mounted on a second layer (insulating layer) of the metal base printed board are individually sealed with the sealing resin.
LED bare chips are known as highly luminous point light sources. In the LED light source unit of Patent Document 1 that is used as a planar light source, luminous parts or high-luminance points comprising separately arranged LED bare chips and a sealing resin covering the chips are visually recognized as “lumpy”. Therefore, discomfort glare is easily produced by luminance unevenness.
In the LED light source unit of Patent Document 1 comprising the reflector with the tapered holes, in particular, the directions of all light components emitted from the luminous parts are regulated by the reflector holes and directly projected downward. Thus, the luminance unevenness is more conspicuous, and hence, produces discomfort glare more easily.
In the case of the LED light source unit of Patent Document 1 that does not use a reflector, it is uncertain whether the discomfort glare attributable to the luminance unevenness can be improved or not. This is because the technique of Patent Document 1 is configured so that an exposed region of the conductor pattern formed on the metal base printed board is covered by the sealing resin with which the LED bare chips are sealed and that other regions of the conductor pattern than the exposed region are not exposed from the printed board. The moisture-proof property of the unit is improved with this arrangement. Thus, the improvement of glare attributable to luminance unevenness is not described at all in Patent Document 1.
Further, the LED light source unit of Patent Document 1 without a reflector is not contrived so that the respective sealed shapes of the individual LED bare chips are uniform, despite the fixed amount of sealing resin used for each chip. Thus, the sealing resin that seals the individual LED bare chips is variously distorted, so that uniform shape, height, etc., cannot be ensured. Therefore, if the LED light source unit includes such sealing resin mixed with the phosphor powder, the luminous parts are different in luminous color. The differences in shape and height between the luminous parts are visually recognized as color unevenness.
The lighting apparatus incorporating the LED light source unit that is liable to the aforementioned luminance or color unevenness has a poor appearance. Therefore, it is advisable to increase the commodity value of the lighting apparatus by improving this point.
Preferably, the lighting apparatus may comprise a translucent cover for use as a guard that prevents a user's hand from touching live parts (wiring pattern, LED bare chips, etc.) or the like. In applications where discomfort glare produced by the LED light source is a problem, therefore, the luminance unevenness or color unevenness can be improved by using a cover with diffusivity suitable for the applications.
Thus, if a milky cover that is the highest in diffusivity is used, for example, the luminance unevenness can be reduced by mitigating the “lumpiness” of the luminous parts based on a light diffusion effect of the cover. If the milky cover is used, however, the luminous fluxes of the lighting apparatus are reduced by 10% when compared with luminaire fluxes produced with use of a transparent cover. Thus, the efficiency of the lighting apparatus is inevitably reduced, all the same.